Clozapine has ben called and "atypical neuroleptic" because it does not induce the characteristic elevations in prolactin levels not does it produce the extrapyramidal reactions common to "classical" neuroleptics. We are conducting a blinded crossover study comparing clinical and biological response of treatment refractory schizophrenics to clozapine versus haloperidol. When enough patients have been studies we will have clinical, neuropsychological, and SPECT studies of each patient on haloperidol, placebo and clozapine. These results may shed some light on the underlying mechanisms for the often unique clinical responsiveness of patients to clozapine. To date four patients have begun this 18 week protocol; none have completed it.